1. Field of the Invention
This invention relates to inertial navigation systems and, more particularly, to such systems of the strap-down type.
2. Description of the Prior Art
All inertial navigation systems provide for the isolation of the accelerometers from rotations of the vehicle. Gyroscopes (gyros) are used for such isolation. In the inertial platform type of system, the gyros drive gimbals which physically isolate the platform-mounted accelerometers from vehicle rotations. In the strap-down type of system, the gyro outputs are coupled to a computer which computationally isolates the outputs of the vehicle-mounted accelerometers from the vehicle rotations to which the accelerometers are physically subjected. Strap-down systems place stringent requirements on the gyro dynamic range performance in maintaining a space fixed reference in a vehicle. A three-axis platform requires three single-degree-of-freedom gyros arranged orthogonally for proper operation. In the prior art, particularly as applied to space vehicles and others where extreme reliability over a considerable period of time is required, the need for redundancy for protection against component failure dictated using at least five gyros to achieve both failure detection and correction. This not only increases the number of gyros required to provide redundancy but it also increases the number of channels including the circuitry for processing the gyro signals.
Recently, a new type of gyro has been developed which provides two degrees of freedom, rather than one. This is a so-called dry tuned rotor gyro and it is possible, in embodiments of the invention shown and described herein, to arrange three two-degree-of-freedom dry tuned rotor gyros or their equivalent in a particular orientation so that both orthogonal and skewed rate data are available with complete redundancy, utilizing only the three units. This affords not only a saving in the number of gyros required, but also a corresponding reduction in the associated circuitry.